1. Field of the Invention
The present invention relates to the sector of optoelectronic rigs, and in particular to their internal architecture. It relates more particularly to a method for optically connecting in an optoelectronic rig, according to a given connection diagram, optical components comprising optical fibers having end sections for mutual connection, and to a rig constructed according to this method.
2. Related Background Art
Optoelectronic rigs are devices used to generate, analyze or modify luminous signals transmitted along a fiber optic line. Rigs of this type are for example optical amplifiers, optical pre-amplifiers, fiber lasers, optical spectrum analyzers, filters and optical switches made in planar optics, etc.
Known in particular are active-fiber optical amplifiers in which the amplifying element consists of a section of optical fiber doped with particular substances, typically rare earths. In this section of fiber, the luminous signal is amplified in optical form using luminous pumping energy provided by laser sources. On occasions the amplification is shared between two stages, and in this case the amplifier comprises two distinct sections of active optical fiber. Optical amplifiers with two stages are known for example from U.S. Pat. No. 5,115,338 and from European patent application EP-A-0509577.
The production of optoelectronic rigs, particularly amplifiers, is often complex.
For example, an active-fiber optical amplifier comprises many electrical, electro-optical and optical components. Among the optical components there are at least one active fiber, one or more optical couplers and possibly optical isolators. Among the electro-optical components there is at least one pumping laser and possibly one or more measurement diodes. The electrical components comprise power supply and control circuits. Locations must be found for all the components within the shell of the amplifier. The electrical components are normally installed on one or more cards, together with the electro-optical components. The layout of the electrical circuits presents no particular problems, and is effected in a manner similar to what occurs in any electrical rig, by means of circuits printed on the same cards or by means of leads soldered to appropriate terminals on the card.
However, because of the structural constraints imposed by the optical fibers, the installing of the optical components is more difficult: active components (active fiber) and passive components (isolators, couplers).
Thus, the optical fibers can be curved only up to a certain minimum radius of curvature, otherwise signal attenuations are produced or damage may even be done to the structure of the fiber. Furthermore, the links between different fibers are made with special rigs which effect an intimate link of the ends of the two fibers by butt fusion bonding, in such a way as to minimize the signal attenuations due to these links; each fusion bond thus effected is encapsulated in a cylindrical protective shell; this makes the fusion bonds akin--for the purposes of their locating in the shell of the amplifier--to passive optical components which likewise are generally of cylindrical shape. Finally, each optical or electro-optical component is provided with pig-tails for connection to the other components; these pig-tails have a certain length so as to allow repeat fusion bonding in the event of errors or repositionings (a component without a pig-tail or with too short a pig-tail can no longer be used) and the shell of the amplifier must therefore provide space to house these pig-tails.
Furthermore, the execution of the butt fusion bonds requires the use of special rigs near the shell of the amplifier. For this purpose also it is necessary that a sufficient length of pig-tail be available to reach this rig from the amplifier in the fitting phase.
The layout of the components inside the shell of an active-fiber optical amplifier has to take all these requirements into account.
Normally, housings are provided for one or more active-fiber spools as are means for partially winding the pig-tails (drums or similar elements); the installation of the remaining components then depends on the installation of the active fiber and of the pig-tails. Often, the various passive components and the fusion bonds are laid out in the shell in a rather disordered manner, and fitting is therefore particularly complex; furthermore, the fixing of the components may prove to be unsure because achieved for example using clips and/or silicone glue.
European patent applications No. EP-A-0595395 and No. EP-A-0595396 describe active-fiber optical amplifiers in which care has been taken over the layout of the components so as to minimize the size of the amplifier, in order to ease its insertion into bays or cabinets. In such amplifiers special seats are provided for the active and passive optical components, for the electro-optical components and for the fusion bonds. The seats are variously laid out inside the shell of the amplifier.
A particular problem is with the fusion bonds between fibers, which are often present in large numbers in the optoelectronic rig (see for example the case of active-fiber amplifiers). Their production and ordered layout inside the rig are often the most difficult phases of the production of the rig.